US 7088958 B2
A communication system (20) includes a hub radio (22) that wirelessly communicates with any number of user radios (24). The hub radio (22) monitors signal quality measurements compiled from the communication signals (30′) transmitted from the various user radios (24) and based upon baseband quadrature constellation point error to estimate out-of-band signal energy for the communication signals (30′). The hub radio (22) formulates commands based upon these measurements that instruct the user radios (24) how to adjust their power amplifier linearizers (66) so that their power amplifiers (74) become better linearized to minimize spectral regrowth and insure compliance with a spectral template.
1. A communication system having remote power amplifier linearization, said system comprising:
at least one user radio having a power amplifier linearizer that applies a transfer function to a modulated data stream, is coupled to a power amplifier, and is configured to transmit a communication signal generated by said power amplifier of said user radio; and
a hub radio configured to receive said communication signal transmitted from said at least one user radio, to generate a signal quality measurement for said communication signal, to formulate commands in response to said signal quality measurement for said communication signal, and to transmit said commands, wherein said one user radio is further configured to adjust said transfer function of said power amplifier linearizer of said user radio in response to one of said commands so that said user radio power amplifier becomes remotely linearized.
2. A communication system as claimed in
3. A communication system as claimed in
said communication system is a digital communication system in which, during each of a series of unit intervals, information is conveyed as a constellation point selected from a constellation of quadrature phase points; and
said hub radio is configured to form said signal quality measurement from baseband quadrature constellation points.
4. A communication system as claimed in
5. A communication system as claimed in
said hub radio comprises a power amplifier for use in communicating with said user radios; and
said hub radio power amplifier is locally linearized.
6. A communication system as claimed in
said communication signals transmitted from said user radio conveys user payload data and system control data; and
said hub radio is configured to generate said signal quality measurement while said communication signal transmits said user payload data.
7. A hub radio for use in a communication system having remote power amplifier linearization, said hub radio comprising:
a receiver section configured to receive a wireless communication signal and to generate a signal quality measurement that is responsive to said communication signal;
a controller configured to estimate a power amplifier linearizer transfer function in response to said signal quality measurement and to formulate a command in response to said estimated power amplifier linearizer transfer function; and
a transmitter section configured to wirelessly transmit said command.
8. A hub radio as claimed in
9. A hub radio as claimed in
said communication signal conveys information during each of a series of unit intervals as a constellation point selected from a constellation of quadrature phase points; and
said receiver section forms said signal quality measurement from baseband quadrature constellation points.
10. A hub radio as claimed in
11. A hub radio as claimed in
12. A hub radio as claimed in
a power amplifier linearizer adapted to apply a transfer function to a modulated data stream and to generate a linearized data stream;
a power amplifier configured to amplify said linearized data stream; and
a local linearization analysis section coupled to said power amplifier linearizer and to said power amplifier to locally linearize said power amplifier.
13. A hub radio as claimed in
14. A user radio for use in a communication system having remote power amplifier linearization, said user radio comprising:
a power amplifier linearizer adapted to apply a transfer function to a modulated data stream and generate a linearized data stream;
a power amplifier configured to amplify said linearized data stream and generate a communication signal;
a receiver section adapted to receive commands from outside said user radio via wireless communication; and
a controller coupled to said receiver and said power amplifier linearizer, said controller being configured to adjust said transfer function in response to said commands so that said power amplifier becomes remotely linearized.
15. In a communication system, a method for remote power amplifier linearization used in generating a communication signal transmitted from a first site for receipt at a second site, said method comprising:
a) receiving said communication signal at said second site;
b) generating a signal quality measurement at said second site, said signal quality measurement being determined from said communication signal received in said receiving activity a);
c) formulating a command at said second site in response to said signal quality measurement;
d) transmitting said command from said second site;
e) receiving said command at said first site;
f) adjusting, at said first site in response to said command, a transfer function applied to a modulated data stream by a power amplifier linearizer;
g) linearizing said modulated data stream in said power amplifier linearizer to generate a linearized data stream;
h) amplifying said linearized data stream in a power amplifier to generate said communication signal; and
i) transmitting said communication signal from said first site.
16. A method as claimed in
17. A method as claimed in
said communication system is a digital communication system in which, during each of a series of unit intervals, information is conveyed as a constellation point selected from a constellation of quadrature phase points; and
said generating activity b) forms said signal quality measurement from baseband quadrature constellation points.
18. A method as claimed in
obtaining ideal constellation points; and
calculating differences between said ideal constellation points and said actual received constellation points.
19. A method as claimed in
20. A method as claimed in
achieving carrier synchronization at said second site prior to said formulating activity c); and
achieving symbol synchronization at said second site prior to said formulating activity c).
21. A method as claimed in
said receiving activity a) receives said communication signal at a receiver section located at said second site;
said method additionally comprises receiving a locally generated calibration signal at said receiver section to determine non-linearity of said receiver;
said method additionally comprises generating said signal quality measurement for said locally generated calibration signal received at said receiver section; and
said formulating activity c) comprises compensating for said non-linearity of said receiver in formulating said command, said compensating activity occurring in response to said signal quality measurement for said locally generated calibration signal.
22. A method as claimed in
23. A method as claimed in
said activities a)–i) form a linearization feedback loop process which repeats to track changes in power amplifier linearization;
during an earlier iteration of said linearization feedback loop process said communication signal is transmitted from said first site at a first power level and a first energy per bit level; and
during a later iteration of said linearization feedback loop process said communication signal is transmitted from said first site at a second power level and a second energy per bit level, said second power level being greater than said first power level and said second energy per bit level being less than said first energy per bit level.
24. A method as claimed in
25. A method as claimed in
said activities a)–i) form a linearization feedback loop process;
said communication signal conveys user payload data and system control data at different times; and
said linearization feedback loop process takes place while said communication signal conveys user payload data.
26. A method as claimed in
receiving said second communication signal at said second site;
generating, at said second site, a second signal quality measurement determined from said second communication signal;
formulating a second command at said second site in response to said second signal quality measurement;
transmitting said second command from said second site;
receiving said second command at said third site;
adjusting, at said third site in response to said second command, a second transfer function applied to a second modulated data stream by a second power amplifier linearizer;
linearizing said second modulated data stream in said second power amplifier linearizer to generate a second linearized data stream;
amplifying said second linearized data stream in a second power amplifier at said third site to generate said second communication signal; and
transmitting said second communication signal from said third site.
The present invention relates generally to the field of communications. More specifically, the present invention relates to the linearization of transmitter power amplifiers.
In the field of communications, and more particularly wireless communications, a transmitter power amplifier generates a communication signal at a power level sufficient for that communication signal to be received at an intended receiver. To the extent that the power amplifier does not have a precisely linear transfer function, the communication signal will include some distortion. This distortion will adversely impact the ability of the receiver to correctly recover the information being conveyed. In digital communications, the adverse impact worsens as communication links attempt to operate at higher modulation orders and lower signal-to-noise ratios.
Moreover, this distortion introduces spectral regrowth into the communication signal. As more and more users vie for the limited electromagnetic spectrum, governmental regulations and system constraints each require communication signals to occupy as little of the spectrum as is necessary for the information being conveyed. Unfortunately, the distortion caused by power amplifier nonlinearities invariably causes the communication signal spectrum to increase.
One historical solution to the power amplifier nonlinearity problem has been to use high quality components or components otherwise restricted to operate only in a limited highly linear range of operation for the power amplifier to minimize spectral regrowth and distortion. Unfortunately, high quality components are too expensive, especially for mass market or otherwise high volume applications. Techniques that restrict operation to highly linear ranges of component operation tend to suffer from inefficient power use and are thus unsuitable for portable applications.
A more modern solution to the power amplifier nonlinearity problem has been to incorporate a power amplifier linearizer into the transmitter. In a typical digital communication application, the linearizer is implemented digitally through the use of look-up tables located upstream of the power amplifier, prior to analog conversion. The linearizer attempts to apply a particular transfer function to the signal it processes. The transfer function is desirably proportional to the inverse of the power amplifier transfer function. Thus, the linearizer predistorts a modulated signal causing the resulting communication signal, that will invariably be distorted by a power amplifier, to be as nearly perfectly linear as possible.
Several conventional techniques are known to those skilled in the art for determining a transfer function to be implemented by a linearizer and generating appropriate data to populate the look-up-tables used by the linearizer. In a typical conventional technique, the transmitter locally monitors and analyzes the communication signal being generated by its power amplifier to determine the nature of the distortion and to track any changes in the distortion. In order to do this, demodulation circuitry is supplied in the transmitter to locally demodulate the communication signal and processing circuitry is supplied in the transmitter to locally analyze the demodulated signal, characterize the distortion, out-of-band energy, or the like, and generate the data used to populate linearizer look-up-tables.
Such conventional linearization techniques suffer from several problems. One problem is that the conventional techniques do not allow the communication system to maintain positive control over spectrum use. Typically, a sample unit of a new radio design is tested in friendly, well-controlled environmental conditions for compliance with a spectral template imposed by governmental regulations. During manufacturing, additional samples may occasionally, although typically rarely, be tested for spectral compliance. This procedure allows numerous opportunities for non-compliant radios to be used by the general public. For example, some radio designs may be non-compliant when used over a range of environmental conditions. In accordance with other radio designs, some radios may be compliant, while others are non-compliant simply due to the vagaries of manufacturing processes. Moreover, some radios may have been compliant at one point in time, but become non-compliant due to component aging. Furthermore, unscrupulous manufacturers of radios may select for testing only those radios likely to prove themselves compliant, may substitute lower quality components for inclusion in manufacturing process when spectral compliance testing is unlikely, and the like. Consequently, many opportunities exist for non-compliant radios to be used by members of the general public.
The use of non-compliant radios is undesirable because it leads to increased interference levels. Increased interference levels diminish the ability of a provider of communication services to provide, and gain revenues from, communication services. Non-compliant radios are also undesirable simply because they are in violation of governmental regulations. Maintaining more positive control would be desirable to communication service providers because they could then insure that their users were using spectrally efficient radios that would minimally interfere with the communication services provided to other users. More communication services could then be provided to more users because interference levels would be diminished, and revenues could increase.
Conventional linearization techniques suffer from additional problems. For example, conventional techniques drive up the complexity and costs of providing communication services, particularly in point to multipoint (PTM) communication systems. A conventional cellular voice communication system is one example of a PTM communication system. In PTM systems, a large number of user radios typically communicate with a single hub radio. The use of conventional linearization techniques at the hub radio may not increase costs an intolerable amount when viewed from a system-wide perspective because those costs are incurred at relatively few sites. On the other hand, the use of conventional linearization techniques in user radios imposes intolerable costs on a communication system because of the large number of user radios that communicate with each hub radio. This cost problem is exacerbated by what has become a traditional business practice where the communication system provider heavily subsidizes the cost of user radios.
These problems are made worse when the user radios are portable. The inclusion of additional demodulation and processing circuitry is highly undesirable in portable radios because these items increase power consumption, weight, and physical radio size.
Another problem with some conventional linearization techniques is that the transmitters are required to transmit predetermined training sequences in order for the local linearization analysis circuitry to determine a suitable linearizer transfer function. The predetermined training sequences are transmitted in lieu of user payload data for which revenues may be generated. Consequently, these conventional linearization techniques diminish a communication service provider's ability to provide communication services to users and revenues that might otherwise be generated.
It is an advantage of the present invention that an improved technique for remote power amplifier linearization is provided.
Another advantage of the present invention is that a communication system is provided where a transmitter in a user radio is remotely linearized in response to processing performed in a hub radio.
Another advantage of the present invention is that linearized user radios are provided without requiring local linearization at the user radios.
Another advantage of the present invention is that a hub radio is provided that can maintain more positive control over the spectrum used by the user radios with which it communicates.
Another advantage of the present invention is that user radios are provided that can use linearized, lower cost, power amplifiers without requiring demodulation and linearization analysis circuitry to accomplish the linearization.
Another advantage of the present invention is that a communication system is provided in which linearization analysis takes place by analyzing a received, noisy, low signal-to-noise ratio communication signal.
Another advantage of the present invention is that a hub radio is provided which includes linearization analysis circuitry and processing capabilities for a number of user radios so that user radios need not include such circuitry and processing capabilities.
These and other advantages are realized in one form by an improved hub radio for use in a communication system having remote power amplifier linearization. The hub radio includes a receiver section configured to receive a wireless communication signal and to generate a signal quality measurement that is responsive to the communication signal. A controller is configured to estimate a power amplifier linearizer transfer function in response to the signal quality measurement and to formulate a command in response to the estimated power amplifier linearizer transfer function. A transmitter section is configured to wirelessly transmit the command.
These and other advantages are realized in another form by a user radio for use in a communication system having remote power amplifier linearization. The user radio includes a power amplifier linearizer adapted to apply a transfer function to a modulated data stream and generate a linearized data stream. A power amplifier is configured to amplify the linearized data stream and generate a communication signal. A receiver section is adapted to receive commands from outside the user radio via wireless communication. A controller is coupled to the receiver and the power amplifier linearizer. The controller is configured to adjust the transfer function in response to the commands so that the power amplifier becomes remotely linearized.
A more complete understanding of the present invention may be derived by referring to the detailed description and claims when considered in connection with the Figures, wherein like reference numbers refer to similar items throughout the Figures, and:
As indicated in
In contrast, system control data 40 represents overhead used to control the operation of communication system 20. Power level adjustments and handoff commands common in voice cellular communication systems represent two of numerous examples of possible system control data 40. Other types of control data are discussed below. System control data 40 is generated and consumed by the components of communication system 20. In accordance with one embodiment of the present invention, communication system 20 performs remote linearization of transmitters in user radios 24 (
Within modulator 52, multiplexer 50 is controlled by controller 48 to supply either user payload data 38 or system control data 40, as deemed appropriate for the operating requirements of the moment, to an input of a phase mapper 54. For each unit interval 42 (
Over time, a stream of constellation points 56 are provided by phase mapper 54 to a pulse shaping filter 60. Desirably, pulse shaping filter 60 implements a root Nyquist or other filter known to those skilled in the art to spread the energy from each constellation point 56 over several unit intervals 42 (
An output of pulse shaping filter 60 is supplied to a peak-to-average amplitude reduction block 62. Block 62 reduces extreme amplitude peaks in the signal being constructed by modulator 52 so that, in addition to other reasons, a power amplifier, discussed below, need not linearly reproduce its input signal over as wide a dynamic amplitude range as would be otherwise required. Block 62 may also be controlled by controller 48 so that the amplitude reduction algorithms may be altered from time to time. Peak to average amplitude reduction block 62 generates a modulated data stream 64 that serves as the output from modulator 52.
Modulated data stream 64 is supplied to a power amplifier linearizer 66. In a manner understood to those skilled in the art, power amplifier linearizer 66 applies a particular transfer function to the signal represented by modulated data stream 64. That particular transfer function is proportional to the inverse of the transfer function of a downstream power amplifier, discussed below, as closely as possible. Linearizer 66 may be implemented using, among other components, a look-up table (not shown) to implement the linearizer transfer function. Accordingly, linearizer 66 couples to controller 48 so that controller 48 may supply the data to this look-up table and adjust this data from time to time.
Linearizer 66 provides linearized data 68 to a digital-to-analog (D/A) converter 70, which couples to an up-conversion block 72. Up-conversion block 72 may also couple to controller 48 so that controller 48 may control frequency tuning and the like. Those skilled in the art will appreciate that upstream of up-conversion block 72, the data processed in transmitter section 46 is desirably represented as complex data streams, and that the complex data streams may then be combined in up-conversion block 72 to produce a single analog signal. This analog signal is provided to an input of a power amplifier 74. Power amplifier 74 amplifies this analog signal to generate a communication signal 30′, which is transmitted from user radio 24 at an antenna 76. In the preferred embodiments, an ordinary cost-effective power amplifier may be used as power amplifier 74. In other words, power amplifier 74 need not exhibit exceptional high quality which might increase expense, and power amplifier 74 need not have excess capabilities which remain unused so that operation may be restricted to a linear range.
Referring back to
The baseband signal generated by RF section 90 is routed to a first input of a phase rotator 92. Phase rotator 92 is used to close a carrier tracking loop that allows receiver section 44 to match and track the carrier frequency used by hub radio 22 (
The signal output from phase rotator 92 is routed to an adaptive equalizer 94. Adaptive equalizer 94 implements a digital filter which adapts itself to compensate for primarily linear distortions in the communication channel. The signal output from adaptive equalizer 94 is routed to a decoder 96 in a demodulator section 98 and to a phase constellation error detector 100. Decoder 96 extracts the conveyed data from the communication signal. Decoder 96 may implement convolutional and/or block decoding and other decoding techniques well known to those skilled in the art in extracting the data from the communication signal. Moreover, decoder 96 is desirably programmable so that it can perform decoding functions which are appropriate for a given modulation order. Such programming may be provided from controller 48.
Within demodulator 98, the data produced by decoder 96 is supplied to a local routing section 102, where user payload data 38 is routed outside user radio 24 and system control data 40 is routed to controller 48. Controller 48 is configured to act upon system control data 40 wirelessly received in receiver section 44. For example, such system control data 40 includes commands which instruct user radio 24 to adjust the transfer function implemented in linearizer 66.
Phase constellation error detector 100 is part of the carrier tracking loop. Phase constellation error detector 100 determines, for each unit interval 42 (
Modulated data stream 116 is routed to an optional power amplifier linearizer 118. Power amplifier linearizer 118 imposes a locally determined transfer function on modulated data stream 116 and thereby generates a linearized data stream 120 supplied to a digital-to-analog (D/A) converter 122. An analog output from digital-to-analog converter 122 passes to an up-conversion section 124. After combining separate complex signals into a single up-converted analog signal, the output from up-conversion section 124 is amplified in a power amplifier 126. Power amplifier 126 amplifies linearized data stream 120 and generates communication signal 30″, which is transmitted to user radios 24 over forward links 26 (
Unlike user radios 24, in one embodiment hub radio 22 is locally linearized. Thus, a local linearization analysis section 128, which is depicted in
In another embodiment, hub radio 22 may omit power amplifier linearizer 118 and local linearization analysis section 128, and instead rely upon the use of high quality components in the construction of power amplifier 126 to insure a desired degree of power amplifier linearity. Such a high quality, linear power amplifier 126 may be a costly item, but since only one hub radio 22 is used for many user radios 24 in a typical application, the cost of that one power amplifier may be spread over a large quantity of provided communication services to have little overall effect on a system-wide basis.
Receiver section 110 includes an RF section 130, phase rotator 132, adaptive equalizer 134, phase constellation error detector 136, carrier tracking loop filter 138, and phase integrator 140 all coupled together and operating substantially as discussed above for user radio 24. Accordingly, communication signals 30′ transmitted from a number of user radios 24 are received and converted into a baseband quadrature constellation point data stream 142 output from adaptive equalizer 134. The assignment of time slots 34 (
Demodulator 144 also provides a data quality signal 145 to controller 112 for use by a remote linearization analysis section 148, discussed below. The data quality signal may, for example, provide an indication of bit error rate (BER), which is readily obtained from decoding circuitry within demodulator 144 in a manner well known to those skilled in the art.
Not discussed above in connection with user radio 24, hub radio 22 includes a constellation error generator 146 having an input adapted to receive baseband quadrature constellation point data stream 142 and having an output coupled to controller 112, and more particularly to remote linearization analysis section 148 of controller 112. Remote linearization analysis section 148 differs from local linearization analysis section 128 because remote section 148 operates upon different parameters extracted from a low signal-to-noise ratio received communication signal 30′ than the parameters used by local section 128, which monitors a high signal-to-noise ratio transmitted communication signal 30″.
CEG signal 162 characterizes the departure of a received communication signal from the ideal. This departure is due to many factors, the most significant of which is typically noise. A secondary factor has been discovered to be non-linear distortion imposed on communication signals 30′ by power amplifiers 74 (
CEG signal(s) 162 provides a statistic that is responsive to an expression of the gain and phase error. During any single unit interval 42, this gain and phase error may be an extremely unreliable characterization of true gain and phase error due to a low signal-to-noise ratio. Thus, filter bank 160 averages the gain and phase errors from a multiplicity of unit intervals 42 to ameliorate the influence of noise. While
Referring back to
Remote linearization analysis section 148 closes a feedback loop that drives non-linear distortion in signals observed in baseband quadrature constellation point data stream 142 to a desired level. It has been discovered that the behavior of CEG signal 162 has good correlation with out-of-band signal energy in communication signal 30′ and little sensitivity to other factors, such as multipath, that might otherwise be present. Consequently, CEG signal 162 serves as the basis of one example of a good signal quality statistic that can be derived and observed to determine the distortion in communication signal 30′. However, any non-linearity which may be present in the components in receiver section 110 of hub radio 22 will cause error in such a signal quality statistic. Consequently, the preferred embodiments compensate for non-linearities in hub receiver section 110.
In one embodiment, high signal quality components are used in the construction of receiver section 110 so that receiver non-linearity is held to a minimum. In this embodiment, coupler 164 may be omitted. While such high quality components may be costly, since only one hub radio 22 is provided for numerous user radios 24, the cost factor may be less significant.
In another embodiment, coupler 164 is used to provide a known substantially linear signal to receiver section 110 from time to time for calibration purposes. The signal routed through coupler 164 is known to be linear due to the local linearization performed at hub radio 24 for power amplifier 126. The same signal quality statistic that is monitored for characterizing non-linearities in communication signals 30′ is monitored for the calibration signal, and the results may be used to offset later readings obtained from communication signals 30′ to compensate for hub receiver section 110 non-linearities. This calibration process may take place while transmitter section 108 is transmitting data to user radios 24 so that no opportunities to provide communication services for users are lost due to the calibration process.
Process 166 includes an initial query task 168 which determines whether transmission has been disabled. Task 168 may, for example, make its determination by evaluating a flag stored in a non-volatile portion of memory. Transmission may have been disabled in response to a command received from hub radio 22. Such a disable command may have been issued if the user radio 24 was transmitting outside its spectral template, and efforts to enforce compliance with the spectral template were ineffective. If transmission is disabled, program control may be viewed as remaining at task 168 for the purposes of the present discussion. Of course, those skilled in the art will appreciate that this situation represents an error condition which an appropriate error trapping routine may address to let the user know that a malfunction has occurred.
When task 168 determines that transmission has not been disabled, a task 170 is performed to control power amplifier 74 (
After task 170, a task 172 controls modulator 52 (
During the initial start-up phase of operating a user radio 24, the relatively high Eb operation will compensate for the relatively low power operation to ensure that communication signal 30′ is adequately received by hub radio 22. However, the data rate will likely be undesirably low. In normal operating conditions, future iterations of process 166 will desirably increase power and lower Eb so that linear, spectral-template-compliant operation at the lowest power level which accomplishes a desired data rate results.
After task 172, a task 174 is performed to cause user radio 24 to engage in normal communications. In other words, referring to
Following task 174, or more precisely while task 174 is ongoing, a query task 176 determines whether receiver section 44 of user radio 24 has received any commands from hub radio 22. Commands represent one form of system control data 40. So long as no commands have been received, program control returns to task 174 to continue engaging in normal communications.
When a command has been received, process 166 progresses to a query task 178 to begin parsing the command. If task 178 determines that a transmit disable command has been received, then a task 180 is performed to set transmission enablement to its disabled state. As discussed above, the transmit disable command may be issued when user radio 24 cannot transmit within the constraints of its spectral template. Following task 180, program control returns to task 168. No further transmissions will emanate from this user radio 24, and the excessive interference that would result from transmitting outside the spectral template will be eliminated. By being able to enforce compliance with the spectral template and by disabling user radios 24 that cannot comply, a hub radio 22 may maintain positive control over the spectrum used by communication system 20 (
When task 178 fails to detect a transmit disable command, a query task 182 determines whether a linearizer adjustment command has been received. When a linearizer adjustment command has been received, a task 184 is performed to adjust the linearizer transfer function, for example from transfer function 82 to transfer function 84 (
When task 182 fails to detect a linearizer adjustment command, a query task 186 determines whether a power adjustment command has been received. When a power adjustment command has been detected, a task 188 controls power amplifier 74 so that future transmissions from user radio 24 will occur at an increased or decreased power level, as instructed by the command. After task 188, program control returns to task 174 to continue engaging in normal communications, but with future transmissions taking place at a different power level. Following initial start-up, where the power level was set to a relatively low level in task 170, the first power adjustment commands received are likely to be for an increased power level. However, as the linearization process continues and during steady state operation, power adjustment commands may indicate either an increased or decreased power level as may be appropriate for the circumstances.
When task 186 fails to detect a power adjustment command, a query task 190 determines whether an energy per bit (Eb) adjustment command has been received. When an Eb adjustment command has been detected, a task 192 controls modulator 52 so that future transmissions from user radio 24 will occur at an increased or decreased Eb level, as instructed by the command. After task 192, program control returns to task 174 to continue engaging in normal communications, but with future transmissions taking place at a different Eb level. Following initial start-up, where the Eb level was set to a relatively high level in task 172, the first Eb adjustment commands received are likely to be for a decreased Eb level. However, as the linearization process continues and during steady state operation, Eb adjustment commands may indicate either an increased or decreased Eb level as may be appropriate for the circumstances.
As indicated by ellipsis in
Process 194 includes a sub-process 196 which gets a revised signal quality measurement from which an updated signal quality statistic is formed. As discussed above, in the preferred embodiment CEG signal 162 (
When task 198 detects synchronization, a query task 200 determines whether any previous commanded parameters are in effect. Task 200 may simply insure that a predetermined amount of time has transpired since a previous command was transmitted to the user radio 24 of interest to be sure that the command has been put into effect. Alternatively, task 200 may determine whether a signal acknowledging receipt of and action upon a command has been received from the user radio 24. Program control remains at task 200 until controller 112 is confident that a previously issued command has been acted upon.
When task 200 determines that a previously issued command has been acted upon, a task 202 clears any averages being calculated for the user radio 24 of interest. By clearing the averages, a new averaging or integrating process is initialized and may then begin. Following task 202, a task 204 transpires while receiver section 110 receives communication signal 30′, and a task 206 simultaneously integrates, filters, or otherwise averages the actual received constellation points 156 conveyed by baseband quadrature constellation point data stream 142. As discussed above, a significant cause of constellation point error is noise, and the averaging of task 206 is performed for a sufficient duration so that a high likelihood exists that the noise influence has been well ameliorated.
Following sufficient averaging in task 206 to ameliorate noise, a task 208 is performed to calculate the non-linearity characteristics and signal quality statistic. Task 208 first adjusts for hub receiver section 110 non-linearities. As discussed above, a calibration process may be performed from time-to-time at hub radio 22 using a known-linear signal transmitted from hub radio 22 as a received communication signal at hub radio 22. Baseband quadrature phase errors resulting from this known-linear signal will correspond to non-linearities resulting from the operation of receiver section 110 in hub radio 22. Task 208 adjusts the constellation error magnitudes obtained from task 206 by subtracting or otherwise compensating for the constellation error magnitudes recorded from the calibration procedure to obtain a signal quality measurement more responsive to non-linearities of the user radio 24 of interest and less responsive to hub radio 22 non-linearities.
In addition to calculating linearization parameters, the signal quality statistic is further developed by combining individual constellation error components, scaling, offsetting, and the like, so that the resulting signal quality statistic may be compared against one or more predetermined thresholds. Below a lower threshold, high and perhaps excessively high compliance with the spectral template is indicated. Between lower and upper thresholds, compliance with the spectral template is indicated, and above the upper threshold, operation outside the spectral template is indicated.
Following task 208, a task 210 determines the latest indication of data quality. Data quality may be determined by simply monitoring the bit error rate signal 145 from a decoder (not shown) portion of demodulator 98. Following task 210, program control returns to process 194 (
Referring to process 194 (
In one state 218, the linearization quality (LQ) obtained above from the operation of sub-process 196 is indicated as being OK, and the data quality (DQ) obtained above from the operation of sub-process 196 is also indicated as being OK. For the purpose of interpreting table 214, an OK linearization quality (LQ) occurs when the signal quality statistic developed in sub-process 196 is between upper and lower thresholds so that spectral template compliance is indicated, but not excessively high compliance. High linearization quality (LQ) corresponds to excessive spectral template compliance, and low linearization quality (LQ) corresponds to non-compliance with a spectral template. When LQ and DQ are both OK, hub radio 22 may simply take an action 216 to maintain the current settings. Such an action may actually amount to taking no action, or a “maintain settings” command may be sent to the user radio 24 of interest to indicate that linearization is being monitored.
In another state 218, LQ is indicated as being high while DQ is OK. In this state 218, hub radio 22 may, if possible, first command a decrease in Eb, which should correspond to operating the communication link at a higher data rate. This action 216 should have little or no detrimental influence on LQ, but may diminish DQ. If successful, this action 216 will allow more spectrum to become available for other users. In addition, if a subsequent hub-command-user-response iteration indicates continued operation in this state 218, hub radio 22 may then command an increase in power so that an increase in data rate is then more likely to be successful. The increase in power command may detrimentally affect LQ, but since LQ is high in this state, it may deteriorate to an OK level without any problem being indicated.
In another state 218, LQ is either OK or High, but DQ is low. In this state 218, hub radio 22 may command an increase in power in an attempt to improve DQ. The command to increase power may cause LQ to deteriorate to a low level, in which case a subsequent iteration of the hub-command-user-response cycle will invoke a different state. If the command to increase power does not cause LQ to significantly deteriorate, and a subsequent iteration of the hub-command-user-response cycle continues in this state, then an increase in Eb may be commanded. An increase in Eb is less likely to deteriorate LQ, but is likely to decrease data rate.
In another state 218, LQ is low and DQ is OK. In this state 218, hub radio 22 may perform a linearize update sub-process 220.
Next, a task 224 is performed to calculate a suitable power amplifier linearizer transfer function that should lead to improved results. Following task 224, a task 226 formulates a linearize adjustment command that is accompanied by coefficients or parameters of the linearizer transfer function determined above in task 224, and task 224 sends the command to the user radio 24 of interest. The command is sent to the user radio 24 of interest via wireless communication over communication signal 30″, (
For tasks 224 and 226, constellation error generator 148 (
Once the residual power amplifier gain and phase error has been estimated, an inverse correction is then calculated for application by user-radio linearizer 66 (
Referring back to
In another state 218, LQ is low and DQ is also low. In this state 218, hub radio 22 may also first perform linearize update sub-process 220 in an attempt to improve the LQ indicator. In conjunction with any linearize adjustment command designed to improve user radio power amplifier linearization, hub radio 22 may issue an increase Eb command to improve DQ. If a subsequent iteration of the hub-command-user-response cycle again returns to the low LQ, low DQ state 218, a decrease power command may be issued in a further attempt to find settings where operation in compliance with the spectral template can take place. If after a predetermined number of repetitions of these actions the LQ continues to indicate a low condition, then the transmit disable command may be issued to prevent the user radio 24 from engaging in future transmissions until the user radio 24 is repaired.
As indicated by ellipsis in
In summary, an improved technique for remote power amplifier linearization is provided. A communication system is provided where a transmitter in a user radio is remotely linearized in response to processing performed in a hub radio. A hub radio is provided that can maintain more positive control over the spectrum used by the user radios with which it communicates. User radios may be commanded to take actions that improve spectral compliance. If spectral compliance is not eventually achieved, user radios may be disabled from transmitting. User radios are provided that can use linearized, lower cost, power amplifiers without requiring demodulation and linearization analysis circuitry to accomplish the linearization. A communication system is provided in which linearization analysis takes place by analyzing a received, noisy, low signal-to-noise ratio, communication signal at a hub radio, and a hub radio is provided which includes linearization analysis circuitry and processing capabilities for a number of user radios so that user radios need not include such circuitry and processing capabilities.
Although the preferred embodiments of the invention have been illustrated and described in detail, it will be readily apparent to those skilled in the art that various modifications may be made therein without departing from the spirit of the invention or from the scope of the appended claims. For example, a communication system in which the present invention is incorporated need not be a point to multipoint system, and it need not implement a TDM communication protocol.